The lymphatic absorption and biliary and urinary excretion of 12 radioactively labelled antitumor agents in the rat has been examined. The compounds studied are C14-CCNU, C14-methyl-CCNU, C14-guanazole, C14-dibromomannitol, C14-diethylstilbestrol, H3-prednisolone, H3-dexamethasone, C14-6-mercaptopurine, C14-cytosine arabinoside, H3-vincristine, C14-cyclophosphamide and C14 o,p-DDD. Results to date indicate that only C14-o,p-DDD is extensively absorbed via the lymphatics. Urinary excretion was the major route of elimination for C14-guanazole, C14-dibromomannitol, C14-6-mercaptopurine, C14-cyclophosphamide, and C14-cytosine arabinoside; C14-diethylstilbestrol, H3-prednisolone, H3-dexamethasone and H3-vincristine were largely excreted via the bile.